In coating automobile bodies and other products, a coating structure has been widely adopted where an undercoat made of a rust-preventing electrodeposition paint, an intermediate coat having the ability to conceal the undercoat, and a topcoat (a base coat and a clear coat) are superposed one upon the other in this order. In order to, e.g., save resources, an attempt has also been made to apply a topcoat directly over an undercoat without an intermediate coat. For example, a base coat having the ability to conceal an undercoat is formed on a cationic electrodeposition coat, and a clear coat is formed on this base coat.
Attempts to allow automobile coatings to have an unprecedented impressive appearance by adjusting the refractive indices of base coats and clear coats are known in the art. For example, Patent Document 1 discloses a technique for allowing the brightness of a coating to change depending on the viewing angle by setting the refractive index of the clear coat to 1.522, while setting a difference between the refractive indices of the base coat and the clear coat to 0.015 or more. Moreover, Patent Document 1 also teaches that an acrylic resin including 50 mass % or more of t-butyl methacrylate exhibits a low refractive index, and that an acrylic resin including 40 mass % or more of styrene exhibits a high refractive index.
Patent Document 2 recites that if ZnO2 nanoparticles are dispersed in a resin, the resin may have an increased refractive index, and also teaches using such a resin as a coating composition.